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lindagy98

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[交流] 欧洲科学家制备出新的单分子磁体

　来自英国、法国、意大利的科学价值辈出基于钴团簇的单分子磁体，单分子磁体在信息存储技术等上有极大应用潜力，但投入应用还有许多工作要做，因为单分子磁体的奇异性质在低温下才能表现出来。
　　据RSC.Org网站2005年10月20日报道：来自英国、法国、意大利的科学价值辈出基于钴团簇的单分子磁体，单分子磁体在信息存储技术等上有极大应用潜力，但投入应用还有许多工作要做，因为单分子磁体的奇异性质在低温下才能表现出来。
　　单分子尺度上的磁性是寻找数字信息记录和存储更有效方式的一关键因素。来自英国、法国和意大利的科学家通过联合攻关，成功制备一种新的单分子磁体（SMM），这种单分子磁体基于多金属钴团蔟（polymetallic cobalt cluste），并表现出奇异的磁性性质
　　通常的磁体的磁性是大量金属中心未配对自旋的平均效应，而SMM单个分子就可以看作一个超小的磁体，可以用来存储信息。理论上讲，每个分子可以存储一比特的信息。每个分子可以存储一比特的信息。SMM 比通常的磁体小很多，意味着更强的信息存储能力，具有明显的巨大商业和产业价值。到现在为止，SMM研究主要基于锰的氧化物团簇，有些研究基于过渡金属如铁和镍。曼彻斯特大学的Richard Winpenny及其来自法国和意大利的同事把钴作为中心金属。钴是一种潜在上很好的SMM候选者，因为它有很不均匀的磁性分布，这样要使磁性丧失需要克服很大的能垒。
　　Richard Winpenny制备了一个含八个钴中心的团簇。研究表明，该团簇磁性丧失有两个不同的弛豫路径。大部分样品显示快速弛豫过程，但是有一小部分弛豫地比较慢，表现出了SMM的行为。科学家相信这有快速磁化开关的潜在用处，但是还有许多工作要做。
　　SMM的一大缺点是，他的奇异磁性质必须在低温下才能表现出来，但是SMM也有许多优于常规磁体之处--------室温制备、科溶于有机溶剂、分子结构易操作性。未来有可能制备出室温下的SMM。
　　研究论文发表在化学通讯（ Chem. Commun ）上。（完）[科研中国SciEi.com瞿立建编译]
来源：英国皇家化学会网站 http://www.rsc.org/chemistryworld/News/2005/October/20100501.asp

原文
A singular attraction
Magnetism on the scale of individual molecules is a key factor in the search for more efficient ways to store and record digital information. In a collaborative effort, scientists from the UK, France and Italy have prepared a new single molecule magnet (SMM) based on a polymetallic cobalt cluster that shows rather unusual magnetic behaviour.

Whereas conventional magnets work because of the bulk effect of the unpaired spins of hundreds of thousands of metal centres, with SMMs, each individual molecule acts as an ultra-small magnet that can be used to store information. Theoretically, this could be one bit of information per molecule. The much smaller size of SMMs compared with traditional magnets means far more information can be stored on hard drives and other devices, with obvious huge commercial and industrial benefits.

The majority of SMMs studied to date are based on manganese oxide clusters, with some studies done on other transition metals such as iron and nickel. Richard Winpenny from the University of Manchester, together with colleagues from the Institut de Chimie de la Matière Condensée de Bordeaux and the Università degli Studi di Firenze & INSTM, have concentrated their efforts on using cobalt as the central metal. Cobalt(II) is a potentially good SMM candidate because it has a large uneven distribution of magnetic properties, resulting in a considerable energy barrier that hampers the loss of magnetization in the material.

Winpenny made a cluster containing eight cobalt centres. Magnetic studies on the cluster revealed two very different relaxation pathways for loss of magnetization—the majority of the sample showed a fast relaxation process, however, a small fraction relaxed slowly, indicative of SMM behaviour. The authors believe that this could be of potential interest for fast switching of magnetization, although more work still needs to be done.

The major drawback for SMMs is that unusual magnetic properties such as these can only be realised at very low temperatures. However, SMMs have a number of advantages over traditional magnets—room temperature synthesis, solubility in organic solvents and the ability to easily manipulate the molecular structure. The future holds great potential for new compounds that show SMM behaviour at higher temperatures.

Stephen B Wilkes
ReferencesS J Langley, M Helliwell, R Sessoli, P Rosa, W Wernsdorfer and R E P Winpenny, Chem. Commun., 2005 (DOI : 10.1039/b510106a)

[ Last edited by lindagy98 on 2005-12-9 at 09:00 ]

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